The present invention relates to a free radical chlorination process for purifying and stabilizing bromine-containing chlorotrifluoroethylene telomers to prepare stable products for use in applications such as for non-flammable hydraulic fluids.
Various methods of preparing chlorotrifluoroethylene ("CTFE") telomers are known in the prior art and have been practiced commercially for many years. An article by William T. Miller, Jr. et al in Industrial and Engineering Chemistry, pages 333-337 (1947), entitled "Low Polymers of Chlorotrifluoroethylene", describes a process for producing low molecular weight polymers of CTFE by polymerization of CTFE in a solution of chloroform using benzoyl peroxide as a polymerization promoter. Other solvents disclosed in the reference as being useful for this purpose include carbon tetrachloride and tetrachloroethylene. The solution is heated in a pressure vessel for 13/4 hours at 100.degree. C., and the unreacted CTFE monomer and chloroform are removed by distillation, leaving a crude telomer of general formula CHCl.sub.2 (CF.sub.2 CClF).sub.n Cl, which can be further heated and distilled to yield products ranging from a light oil to a semi-solid wax or grease.
Another process for preparing low molecular weight CTFE polymers is described in U.S. Pat. No. 2,788,375, issued Apr. 9, 1957. This process involves reacting CTFE with a saturated brominated compound in the presence of a source of radiation. Suitable brominated compounds include bromotrichloromethane and 1,2-dibromo-2-chlorotrifluoroethane (CF.sub.2 BrCClFBr). The saturated bromopolychlorofluoro compounds obtained by this process are then distilled, and the isolated fractions reacted with chlorine in the presence of tungsten light, at 150.degree. C. to 250.degree. C., such as supplied by a tungsten filament lamp, to prepare the corresponding polychlorofluoro compounds. The process disclosed in this patent is not a selective chlorination process since it results in the chlorination of both the telomer species and the organic impurities, and therefore does not assist in the separation and purification of the telomer species.
It is therefore a principal object of the present invention to provide an improved process for purifying and stabilizing bromine-containing telomers which can be used as non-flammable hydraulic fluids.